This core has continued progress in 3 areas: continued development of TmDOTP5- for quantitation of intracellular sodium, new synthetic chemistry to generate new reporter ligands for divalent cations, and initial clinical applications of the magnesium indicators. Applications of TmDOTP5- were described in the "highlights" section of this report, and the new synthetic chemistry work was described in the research overview. The measurement of free magnesium by ion sensitive electrodes is difficult but is highly relevant to a number of disease states, and the relations among total magnesium (TMg), ionized magnesium (iMg), and NMR measured magnesium (nmr-Mg) provides information about Mg compartmentation in plasma. Therefore, a commercial ion sensitive electrode has been installed in this lab for rapid comparison with the NMR results from NOTMP, to measure ionized Mg2+ levels in adult blood plasma by 31P NMR. Our first observations indicate that the difference between TMg and nmr-Mg provides an estimate of the tight protein bound Mg2+ fraction (pMg). We are currently using these methodologies to examine the distribution of Mg2+ in plasma from pregnant women who experienced premature labor after 24-32 weeks gestation (prior to treatment with MgSO4 to halt premature labor). TMg (0.68 q 0.13) was significantly lower than in non-pregnant adults, while nmr-Mg (0.58 q 0.09) and iMg (0.48 q 0.05) only showed a trend toward lower values. The similarity between TMg and nmr-Mg suggests that pMg is lower in these women compared to controls. (Collaborative 1) REPORT PERIOD: (09/01/97-08/31/98)